This invention is generally directed to photoresponsive imaging members, and more specifically the present invention is directed to layered photoresponsive imaging members with a charge transporting layer comprised of certain charge transporting polyurethanes. Thus, in one embodiment the present invention relates to an imaging member comprised of a photogenerating layer, and a charge or hole transport layer comprised of charge transport polyurethanes. Further, in another embodiment of the present invention there is provided an imaging member comprised of a supporting substrate, a hole transport layer comprised of fluorene-based polyurethanes of the formulas illustrated herein, and situated therebetween a photogenerating layer. Additionally, the present invention includes within the scope thereof imaging members wherein the photogenerating layer is situated between the hole transporting layer, and the supporting substrate. The photoresponsive imaging members of the present invention are useful for incorporation into various imaging systems, particularly xerographic imaging processes wherein, for example, the members are initially charged negatively, and development is accomplished by dry or liquid developer compositions. Also, the aforementioned novel charge transporting polyurethanes of the present invention possess excellent hole transport properties; are substantially resistant to liquid and dry developer compositions in that, for example, they are free of crystallization, a disadvantage associated with many prior art hole transport compounds such as those illustrated in U.S. Pat. No. 4,265,990 when liquid developers are selected; and further with the polyurethanes of the present invention resinous binders can be avoided. Furthermore, the layered photoresponsive imaging members of the present invention are durable, possess acceptable dark decay characteristics, and are insensitive to changes in environmental conditions such as humidity and temperature. Also, the polyurethanes of the present invention can be formed into films enabling, for example, flexible imaging belts, including seamless belts. Moreover, the polyurethanes of the present invention can be readily synthesized by known economic processes.
The generation and development of electrostatic latent images on the surfaces of photoconductive members by electrostatic means is well known. One electrostatic method involves the formation of a latent image on the surface of a photoreceptor. These photoreceptors can be comprised of a conductive substrate containing on its surface a layer of photoconductive insulating material, and in many instances there can be incorporated therein a thin barrier layer between the substrate and the photoconductive layer to prevent charge injection into the photoconductive layer upon charging of its surface, which injection would adversely affect the quality of the resulting image.
Numerous different xerographic photoconductive members are known including, for example, a homogeneous layer of a single material such as vitreous selenium, which can function as both a photogenerating and hole transporting substance, or composite layered devices with a photoconductive substance dispersed in other substances. An example of one type of composite photoconductive layer used in xerography is described, for example, in U.S. Pat. No. 3,121,006 wherein there is disclosed a number of layers comprising finely divided particles of a photoconductive inorganic compound dispersed in an electrically insulating organic resin binder.
As more advanced, higher speed electrophotographic copiers, duplicators and printers were developed, degradation of image quality was encountered during cycling. Moreover, complex, highly sophisticated duplicating and printing systems operating at high speeds have placed stringent requirements including narrow operating limits on photoreceptors. For example, the numerous layers found in many modern photoconductive imaging members must be highly flexible, adhere well to adjacent layers, and exhibit predictable electrical characteristics within narrow operating limits to provide excellent toner images over many thousands of cycles. There is also a current need for long service life, flexible photoreceptors in compact imaging machines that employ small diameter support rollers for photoreceptor belt systems compressed into a very confined space. Small diameter support rollers are also highly desirable for simple, reliable copy paper stripping systems which utilize the beam strength of the copy paper to automatically remove copy paper sheets from the surface of a photoreceptor belt after toner image transfer. However, small diameter rollers, for example, less than about 0.75 inch (19 millimeters) diameter, raise the threshold of mechanical performance criteria for photoreceptors to such a high level that spontaneous photoreceptor belt material failure becomes a frequent event for flexible belt photoreceptors.
There are also known photoreceptor members comprised of other inorganic or organic materials wherein the charge carrier generation and charge carrier transport functions are accomplished by discrete contiguous layers. Additionally, photoreceptors are disclosed in the prior art which include an overcoating layer of an electrically insulating polymeric material, and in conjunction with this overcoated type photoreceptor there have been proposed a number of imaging methods.
Specifically, there have been disclosed layered photoresponsive imaging members comprised of photogenerating layers and aryl amine hole transport layer, in U.S. Pat. No. 4,265,990, the disclosure of which is totally incorporated herein by reference. Examples of photogenerating layers include trigonal selenium and phthalocyanines, while examples of the active transport layer molecules that may be employed are comprised of the aryl amines illustrated in the '990 patent. The imaging members of the present invention may be considered similar to those described in the aforementioned patent with the primary exception that there are selected in place of the aryl amines the fluorene polyurethanes illustrated herein, which polyurethanes possess the improved characteristics disclosed herein, including permitting the rapid transport of holes, and no or minimal crystallization with dry, or liquid developer compositions. Also, the fluorene charge transport polyurethanes of the present invention can be selected for layered imaging members wherein a resinous binder is eliminated. Furthermore, the hole transport polyurethanes of the present invention possess excellent compatibility with common optional polymer binders such as polycarbonates, polyesters, poly(methyl methacrylate), polystyrene copolymers, and the like, thus ensuring excellent long-term stability of the transport layers. In addition, the polyurethane charge transport layers of the present invention can be further doped with suitable fluorene charge transport small molecules to enhance the transport capability for high speed printing and copying processes. Moreover, the hole transport polyurethanes selected for the imaging members of the present invention can be economically obtained by simple synthetic processes, and wherein the polyurethane products resulting are of exceptionally high purity thus enabling them to be very suitable for xerographic imaging methods.
Isopar, commonly employed in liquid developer inks, can substantially degrade the mechanical integrity and electrical properties of layered photoreceptors. More specifically, the organic carrier fluid of a liquid developer tends to leach out activating small molecules, such as the arylamine containing compounds typically used in the charge transport layers. Representative of this class of materials are: N,N'-diphenyl-N,N'-bis(3-methylphenyl)-[1,1'-biphenyl]-4,4'-diamine; bis-(4-diethylamino-2-methylphenyl)-phenylmethane; 2,5-bis-(4'-dimethylaminophenyl)-1,3,4, -oxadiazole; 1-phenyl-3-(4'-diethylaminostyryl)-5-(4"-diethylaminophenyl)-pyrazoline; 1,1-bis-(4-(di-N,N'-p-methylphenyl)-aminophenyl)-cyclohexane; 4-diethylaminobenzaldehyde-1,1-diphenylhydrazone; 1,1-diphenyl-2(p-N,N-diphenyl amino phenyl)-ethylene; and N-ethylcarbazole-3-carboxaldehyde-1-methyl-1-phenylhydrazone. The leaching process results in crystallization of the activating small molecules, such as the aforementioned arylamine compounds, onto the photoreceptor surface and subsequent migration of arylamines into the liquid developer ink. In addition, the ink vehicle, typically a C10-C14 branched hydrocarbon, induces the formation of cracks and crazes in the photoreceptor surface. These effects lead to copy defects and shortened photoreceptor life. The degradation of the photoreceptor manifests itself as increased background and other printing defects prior to complete physical photoreceptor failure. The leaching out of the activating small molecule also increases the susceptibility of the transport layer to solvent/stress cracking when the belt is parked over a belt support roller during periods of non-use. Some carrier fluids also promote phase separation of the activating small molecules, such as aryl amine compounds and their aforementioned derivatives, in the transport layers, particularly when high concentrations of the arylamine compounds are present in the transport layer binder. Phase separation of activating small molecules also adversely alters the electrical and mechanical properties of a photoreceptor. Although flexing is normally not encountered with rigid, cylindrical, multilayered photoreceptors which utilize charge transport layers containing activating small molecules dispersed or dissolved in a polymeric film forming binder, electrical degradation is similarly encountered during development with liquid developers. Sufficient degradation of these photoreceptors by liquid developers can occur in less than eight hours of use thereby rendering the photoreceptor unsuitable for even low quality xerographic imaging purposes. These disadvantages are avoided or minimized with the imaging members of the present invention.
Photoreceptors have been developed which comprise charge transfer complexes prepared with polymeric molecules. For example, charge transport complexes formed with polyvinyl carbazole are disclosed in U.S. Pat. Nos. 4,047,948; 4,346,158 and 4,388,392. Photoreceptors utilizing polyvinyl carbazole layers exhibit relatively poor xerographic performance in both electrical and mechanical properties. Polymeric arylamine molecules prepared from the condensation or secondary diamine with a di-iodo aryl compound are disclosed in European Pat. No. 34,425, published Aug. 26, 1981, issued May 16, 1984. Since these polymers are extremely brittle and form films which are very susceptible to physical damage, their use in a flexible belt configuration is generally precluded.
Other prior art includes Canadian Pat. No. 1,171,431, corresponding to European Pat. No. 34,425, published Aug. 26, 1981, issued May 16, 1984, which describes condensation polymers of a secondary diamine with a di-iodo arly compound, for example, in working Examples IX and X;
Photoconductivity and Hole Transport in Polymers of Aromatic Amine-Containing Methacrylates, Journal of Polymer Science: Polymer Chemistry Edition, Vol. 21, 969 (1983), wherein hole transport is described for high molecular weight arylamine-substituted polymethacrylates; synthesis of the monomers, their polymerization, and the general properties of the polymers are also discussed;
U.S. Pat. No. 4,052,205, issued Oct. 4, 1977, discloses a photoconductive imaging member comprising various active polymers, such as poly-N-vinyl carbazole, in a transport layer, see line 45, column 5 to line 27, column 6. Derivatives of the active polymers may be hydroxy substituted, reference column 5, lines 62 to 5;
U.S. Pat. No. 4,265,990, issued May 5, 1981, discloses transport layers comprising small molecule arylamines and a polycarbonate resin binder;
U.S. Pat. No. 4,415,641, issued Nov. 15, 1983, discloses an electrophotographic light-sensitive element comprising a carbazole derivative (see column 3, lines 1 to 14);
U.S. Pat. No. 4,588,666, issued May 13, 1986, discloses a hole transporting molecule comprising alkoxy derivatives of tetra phenyl biphenyl diamine (see column 3, lines 33-66); R.sub.1 and R.sub.2 can represent alkoxy groups which include methoxy. Resins such as polyvinyl carbazoles, polycarbonate resins, epoxy resins, polyvinyl butyrals, polyhydroxyether resins may be used as a binder for the hole transporting molecule;
U.S. Pat. No. 4,047,948, issued Sept. 13, 1977, discloses a photoreceptor comprising layers which may contain polyvinyl carbazole. The use of small molecule arylamine activating compounds in transport layers is also disclosed;
U.S. Pat. No. 4,346,158, issued Aug. 24, 1982, discloses a photoreceptor comprising layers which may contain polyvinyl carbazole. The use of small molecule arylamine activating compounds in transport layers is also disclosed. The preferred small molecule resin binder is a polycarbonate resin;
U.S. Pat. No. 4,388,392, issued June 14, 1987, discloses a photoreceptor comprising layers which may contain polyvinyl carbazole. The use of an electron-donating polycyclic aromatic hydrocarbon incorporated in an electron-donating polymeric photoconductor in a charge transporting layer is also disclosed;
U.S. Pat. No. 4,273,846, issued June 16, 1981, discloses an imaging member comprising a polycarbonate resin material and an arylamine (see the general formula, column 2, lines 21 to 34). Poly-N-vinyl carbazole may be employed in the generator layer;
U.S. Pat. No. 3,844,781, issued Oct. 29, 1974, discloses various photoconductive materials containing substituents such as hydroxyl, amino and alkoxy groups;
U.S. Pat. No. 3,890,146, issued June 17, 1975, discloses various photoconductive materials containing substituents such as hydroxyl, amino and alkoxy groups; and
U.S. Pat. No. 4,588,667, issued May 13, 1986, discloses various overcoated electrophotographic imaging members including a multilayered imaging member having a substrate, a titanium metal layer, a siloxane blocking layer, an adhesive layer, a charge generating binder layer, and a charge transport layer. The transport layer may contain from about 25 to about 75 percent by weight of arylamine transport material in a resin binder such as polycarbonate resin.
Other representative prior art disclosing layered photoresponsive devices include U.S. Pat. Nos. 4,115,116; 4,047,949; 4,081,274 and 4,315,981. According to the disclosure of the '981 patent, the recording member consists of an electroconductive support, a photoconductive layer of organic materials which contain a charge carrier producing dyestuff layer of a compound having an aromatic, or heterocyclic polynuclear quinone ring system, and a charge transport layer.
Furthermore, there is disclosed in U.S. Pat. No. 4,135,928 electrophotographic light sensitive members comprised of 7-nitro-2-aza-9-fluorenylidene-malononitrile as charge transporting substances. According to the disclosure of this patent, the electrophotographic light sensitive members are comprised of an electroconductive support, a layer thereover of a photogenerating substance, and 7-nitro-2-aza-9-fluorenylidene-malononitrile of the formula, for example, as illustrated in column 1. There are also disclosed in U.S. Pat. No. 4,474,865 imaging members with electron transporting layers of fluorenylidene derivatives. In addition, there are also known layered photoresponsive imaging members wherein there are selected hole transport layers of aryl amines, and various photogenerating squaraine compounds, reference for example U.S. Pat. Nos. 4,552,822; 4,415,639; 4,471,041 and 4,486,520.
There are also illustrated in U.S. Pat. No. 4,618,551, the disclosure of which is totally incorporated herein by reference, photoresponsive imaging members with photogenerating layers, and charge transport layers comprised of polysilylenes. More specifically, there is illustrated in the aforementioned patent a polysilylene hole transporting compound for use in imaging members, which compound is of the formula as illustrated in claim 1 with specific examples of polysilylenes being poly(methylphenylsilylene) of an average molecular weight of greater than 50,000.
Also of interest is U.S. Pat. No. 4,106,934, which illustrates photoconductive insulating compositions containing one or more p-type organic photoconductor components and a charge transfer complex of one or more electron acceptor components of the formulas as illustrated in the Abstract, for example. Particularly useful as Formula 1 type compounds are those materials as illustrated in column 5, beginning at line 30. Further, the use of N-substituted polymeric acrylic acid amides and alpha-alkyl acid amides as overcoatings for photoconductors is illustrated in U.S. Pat. No. 3,307,940 (see Formula 5, column 2). Moreover, fluorenylidene derivatives as charge transporting compounds in photoreceptors are disclosed in U.S. Pat. Nos. 4,400,455; 4,245,021; 4,415,640; 4,559,287 and 4,562,132. In addition, U.S. Pat. No. 3,615,412 discloses organic photoconductors with certain fluorenes fused to benzo and naphtho ring structures, reference columns 1 to 3.
In addition, of interest is copending application U.S. Ser. No. 061,247, filed June 2, 1987, which illustrates a layered photoresponsive imaging member comprised of a photogenerating layer, and in contact therewith a hole transporting layer comprised of fluorene derivatives of the following formula dispersed in an inactive resinous binder: ##STR2## where R and R' are independently selected from the group consisting of hydrogen, alkyl, and substituted alkyl groups; and Ar and Ar' are independently selected from the group consisting of aryl and substituted aryl substituents. The following patent applications and U.S. patents are mentioned: (1) U.S. Ser. No. 07/061,064 discloses layered imaging members with novel polymeric, hydroxy and alkoxy aryl amines, wherein m is a number of between about 4 and 1,000, reference for example claims 1 and 2; (2) U.S. Ser. No. 061,247 and U.S. Ser. No. 07/198,254 illustrate imaging members with novel dihydroxy terminated aryl amine small molecules, reference claims 1 and 2, for example, (3) U.S. Pat. No. 4,806,444, the disclosure of which is totally incorporated herein by reference, describes layered imaging members with novel polycarbonate polymeric arylamines, reference claims 1 and 2, for example; (4) U.S. Pat. No. 4,806,443, the disclosure of which is totally incorporated herein by reference, illustrates novel polycarbonate polymeric amines useful in layered imaging members, reference claims 1 and 2, for example; and (5) U.S. Pat. No. 4,801,517, the disclosure of which is totally incorporated herein by reference, which discloses imaging members with novel polycarbonate arylamines, reference claims 1 and 2, for example.
In U.S. applications U.S. Ser. No. 274,159 and U.S. Ser. No. 274,160 entitled, respectively, PHOTOCONDUCTIVE IMAGING MEMBERS WITH N,N-BIS(BIARYLYL)ANILINE, OR TRIS(BIARYLYL)AMINE CHARGE TRANSPORTING COMPONENTS, and PHOTOCONDUCTIVE IMAGING MEMBERS WITH BIARYLYL DIARYLAMINE CHARGE TRANSPORTING COMPONENTS, the disclosures of which are totally incorporated herein by reference, there are described layered photoconductive imaging members with transport layers incorporating biarylyl diarylamines, N,N-bis(biarylyl)anilines, and tris(biarylyl)amines as charge transport compounds. In the above-mentioned applications, there are disclosed improved layered photoconductive imaging members comprised of a supporting substrate, a photogenerating layer, optionally dispersed in an inactive resinous binder, and in contact therewith a charge transport layer comprised of the above-mentioned charge transport compounds, or mixtures thereof dispersed in resinous binders.
The fluorene polyurethanes of the present invention differ from the aforesaid charge transport compounds in that, for example, the invention charge transport polymer systems are derived from fluorene hole transport structures. More importantly, the charge transport moieties of the polymers of the present invention are covalently bonded to the backbones via the C-9 carbon atom of the fluorene structure, and are pendent to their polymer backbones. The fluorene transport moieties are forced into assuming an intimate face-to-face stereochemical relationship resulting in optimum electronic interactions between these fluorene moieties. The close interactions as described herein promote and enhance the overall charge transport capability of these charge transport polymeric systems. In contrast, the transport moieties of many of the above cited applications form an integral part of their polymer backbones, thus drastically inhibiting these structures from close electronic interaction.
Although imaging members with various hole transporting substances, including arylamines and polysilylenes, and the amines and anilines of U.S. Ser. Nos. 274,159 and 274,160 are suitable for intended purposes, there continues to be a need for the development of improved members, particularly layered members which are comprised of fluorenebased polyurethane transport layers; and which members are inert to crystallization and insensitive to the changes in environmental conditions. Moreover, there continues to be a need for specific layered imaging members which not only generate acceptable images, but which can be repeatedly used in a number of imaging cycles without deterioration thereof from the machine environment or surrounding conditions. Additionally, there continues to be a need for improved layered imaging members wherein the materials employed for the respective layers, particularly the hole transporting layer, are substantially inert. Further, there continues to be a need for improved photoresponsive imaging members, which can be prepared with a minimum number of processing steps, and wherein the layers are sufficiently adhered to one another to allow the continuous use of these members in repetitive imaging processes. There also is a need for new hole transporting substances with excellent charge transport mobilities. Likewise, there is a need for hole transporting layers with increased stability, for example, wherein there is essentially no bleeding and segregation or crystallization of transport molecules after an extended number of imaging cycles. Furthermore, there is a need for hole transporting polymers useful in layered imaging members, which polymers are superior insulators in the dark compared to many other known hole transporting compounds, thus enabling charging of the resulting imaging member to higher fields while maintaining cyclic stability, and allowing improved developability, especially with liquid developer compositions. Additionally, there is a need for enabling the preparation of imaging members with new hole transporting polymers wherein the preparation allows for the selection of a variety of solvents, inclusive of toluene, benzene, tetrahydrofuran, cyclohexane, and halogenated solvents in addition to methylene chloride. There is also a need for imaging members with improved electrical characteristics, and comprised of hole transporting fluorene polyurethanes, which members can be positively or negatively charged depending on the configuration of the member. Another need of the present invention resides in the provision of a novel class of hole transport polyurethanes whose physical, electrical and electrochemical properties can be modified by altering the two amino substituents on the fluorene structure. Moreover, there continues to be a need for synthetic processes for the preparation of fluorene hole transporting polyurethanes useful in the layered imaging members of the present invention. There is also a need for imaging members wherein there can be selected the charge transporting polyurethanes illustrated herein, which polyurethanes need not be dispersed in resinous binders.